During the year in progress new findings have emerged on the properties of protein kinase activity associated with peripheral nerve myelin and the effect of diabetes on it. Protein components of myelin prepared from rat sciatic nerves were phosphorylated when gamma-P32 ATP was incubated with a highly purified preparation of this membrane, indicating the presence of both the substrate (receptor protein) and an endogenous kinase in the membrane. Polyacrylamide gel electrophoresis of the phosphorylated membrane proteins followed by scintillation counting of gel slices and autoradiography showed that the polypeptides of molecular weights 28,000, 23,000 and 19,000 were phosphorylated. Among these the polypeptide of molecular weight 19,000, present in relatively phosphorylation of membrane proteins, P32 from gamma-P32 ATP was transferred to serine residues of the substrate proteins. Phosphorylation of purified myelin was Mg ion dependent and had an optimal at pH 6.5 and was not stimulated by cAMP. Exogenous proteins, such as phosvitin, casein, protamine and histone, can also act as substrate for the membrane associated kinase. Rabbit muscle protein kinase inhibitor had no effect on the endogenous phosphorylation of myelin proteins or on the phosphorylation of phosvitin by peripheral nerve myelin protein kinase was inhibited by protein kinase inhibitor. After washing the membrane with 150 mM KC1 the protein kinase that utilized histone as substrate was found in the supernatant. In contrast, the endogenous phosphorylation of membrane proteins or the phosphorylation of phosvitin by the membrane associated kinase was not affected. BIBLIOGRAPHIC REFERENCES: Spritz, N., H. Singh, and B. Marinan. Metabolism of Peripheral Nerve Myelin in Experimental Diabetes. J. Clin. Invest. 55, 1049-56 (1975). Spritz, N., H. Singh and B. Marinan. Decrease in Myelin Content of Rabbit Sciatic Nerve with Aging and Diabetes. Diabetes. 24, 680-3. (1975).